Add metadata attribute to Model class

[SeanBryan51]

The following code can be encapsulated within a metadata attribute associated with each model instance:

benchcab/src/benchcab/fluxsite.py

Lines 266 to 267 in 9034b12

	"cable_branch": self.model.repo.get_branch_name(),
	"svn_revision_number": self.model.repo.get_revision(),

This is useful for reusing the Model class within the context of spack. Spack installed models will have different metadata attributes, e.g the name, version and hash of the package, which should be recorded in the model outputs.